Weak Ships???

[Alan D. Hyde]

Here's an interesting article suggesting that current construction of bulk carriers may be insufficiently strong to resist certain storm and wave conditions...

http://news.bbc.co.uk/1/hi/uk/england/1675801.stm

If ACB reads this, I'd be particularly interested in his views. And, we have several N/A's here. Is the article accurate?

Alan

[ 08-21-2002, 10:46 AM: Message edited by: Alan D. Hyde ]

[thechemist]

I had always thought that such could happen, just based on the physics of the situation. A ship one wavelength long would have water pushing up under one half and dropping out from below the other half, stretching the higher half and compressing the lower half. The stresses would be extremely severe. I read somewhere that waves in the open ocean tended to have some particular wavelength......seventy feet, I think. Thus, vessels much longer or shorter tended not to experience such severe stresses.

[Jim H]

This might explain what happened to the Edmund Fitzgerald. C.G. said the hatches were not properly latched, but this seems to be the same type of vessel.

[Donn]

"I read somewhere that waves in the open ocean tended to have some particular wavelength......seventy feet, I think."

I don't know about that. It's hard for me to believe that there is a norm, or tendency in wavelength. There are so many factors that would/could affect wavelength..weather, undersea earthquakes, solar and lunar anomalies, shifting primary currents, thermoclines. The construction of waves are susceptible to so many variable harmonic distortions...it ain't like the wave tank in physics class.

The conversation going on in the "hydrodynamics of rips" thread is a fascinating one. The combination of water temperature, current, tidal flow and shoal water is almost unpredictable. Only years of experience dealing with the variables and their effects can yield accurate prediction.

It's the old problem that artificial intelligence has faced since it became a reality. How do you get the expert experiences out of the experts, and into the neural net? The art of the science seems to be the patterning of the questioning.

[Ross Faneuf]

Wave lengths in the open ocean are a function of fetch and duration of the wind. Wave length and height are related (I don't have the mathematical formula at hand, but it dates back many decades), so that if you know the wave height, you know the wave length, and vice versa. This changes when the sea shallows; when the bottom is within about wave height x 20, the length begins to decrease and the height increase. Things also change when waves begin to break, as can happen even in the open ocean.

Maximum wave lengths are more on the order of 1000s of feet for really big waves. Vague memory suggests the 70' wave length is associated with 8-10' height.

If you are thinking height, not length, then 70' is a VERY big wave, but not the biggest. There have been a few measurements of open-sea storm waves in the 90-100' range, and a few terrified observations of bigger ones. A wave broke clean over the old Boston light, which was well over 100'; but breaking waves are higher.

It's interesting that the problem with large bulk carriers may be more that the hatches can't take it than that the hull can't take it. Typical failure seems to be not that the hull girder fails (which is the condition that they're designed for), but that a component fails or the shell is breached, after which the ship doesn't have a chance.

I was a naval arch student way long ago, and the standard hull strength calculation was based on poising a ship on a wave of its own length - once with the crest midships, once with the trough midships, and designing for that condition. That criterion dates back at least to the 1930s. Hopefully, it's still done - unless designers of bulk carriers are assuming that they won't encounter a wave of such size. But it's still possible for a hull to fail even when the nominal strength is adequate through progressive failure initiated by a failed component.

[Dave Fleming]

something like this? http://www.imagestation.com/picture/sraid29/p1483e7802333fb06f6f2a46ea4f50788/fd6026b7.jpg

[On Vacation]

Dave, been there, done that. Yes a picture is surely worth a thousand words. But sometimes even a hundred words and pictures will never make a believer out of a few. smile.gif

[ 08-20-2002, 08:47 PM: Message edited by: oyster ]

[Dave Fleming]

http://www.imagestation.com/picture/sraid29/pc6ba05062e84852659ae6b9f74bb5814/fd60233f.jpg

Good air shot of the in distress, sailing yacht during the 'Perfect Storm' rescue.

IIRC, after abandoning the vessel, it was later found washed up on a beach in southeastern US., relatively unharmed from the experience.

[ 08-20-2002, 09:05 PM: Message edited by: Dave Fleming ]

[paladin]

It seems that a well designed offshore yacht is capable of surviving much more than the average human body. Back in the late 60's I wuz in a storm (definitely not planned) that sank two large freighters and a 50 foot Cheoy Lee but left my 31 foot tri untouched and me with lotsa bruises....I trailed a bridle and a long drogue from the forward ama positions, tied everything down and went below with some hot soup.....and slept......

[Paul Scheuer]

Two items. Does the inflexability of the bulk cargo have anything to do with it ? I remember Saratoga twisting what looked to me like several feet over her length, in moderate open ocean swells. She was only 88K tons, though.

Also. Take a look at what goes through the Canal on a regular basis. Scares me. (It's a live camara, so you see more during their day.) http://www.pancanal.com/eng/photo/camera-java.html

[Dave Fleming]

Palidin, I got a notion that the human factor has a big part in the survival of a vessel more our size.
The motion, in my limited experience is much more extreme and the length of the heavy weather compounds the discomfort for many folks.
Granted there are some that can just sip some soup and take a nap whilst the winds do howl and the seas do roar but I'm betting that for every one of us that can take that( or could, ahem ) there are many more that cannot and will loose common sense and just give up.
My most extreme experience in heavy weather was on a USCG WAVP, a 311 foot vessel. We did get caught in the dangerous semi-circle of an Atlantic hurricane. Spuntnik had just been launched to give you a time frame. I would say that of over 200 personel on that vessel there were less than 30 all told who were able to man stations. 2 men on wheel for 15 minutes and then another 2 would relieve them. Taking it green over the 5 inch gun turret and smashing into the pilot house windows. Luckly none were breached.
The worst of it was the up and down motion as we headed into the swells. Deceptively smooth as the wind velocity swept the crests off of them but the motion was very tireing. Prop would come out of the water with every passing wave and the whole vessel would shudder as the vibrations were transferred to every piece of the ship. Light bulbs burst, insulation breaking loose and floating in the air like a thick brown fog, no hot food for at least 3 days and much else.
Me, silly romantic, I was in seventh heaven!
MOTHER, the deep blue as I call it, never really frightned me. I was in awe of the continued power and intensity of the storm but perhaps because of my age or whatever...was never in fear of my own life. Respectfull you damm tooting but not scared.
Ayup one crazy rum swilling Irishman, am I.

[Bayboat]

It's just about axiomatic that a well found and well handled small sailing boat has a better chance of surviving a severe storm than a large vessel. The small boat rolls with the punches, whereas the large one suffers a lot of damage when waves come aboard and find resistance. I've been on both during storms many times and always felt more secure on the small one.

[Ross Faneuf]

There are lots of ways for a vessel to fail and sink. Most modern construction, including welded steel/aluminum, fiberglass and its variants, cold molded - all constructions which create a monocoque hull - don't usually fail because of an initial failure of the hull shell. Same is true of the kind of small boats we mostly own/aspire to. Failure is usually due to a point or component failure after which there is either flooding which can't be controlled, or succesive failures leading to flooding etc. I remember reading with some anguish of the loss of a sizeable sailing yacht - 60ish feet - which sank due to progressive flooding on a trip to Bermuda. The boat had received an extensive refit and then was bought by a new owner. A thru-hull failed, and the owner wasn't too familiar with the boat's layour, and couldn't locate the failed thruhull. There are other details (the engine was flooded and couldn't be run, thus the high-capacity dewatering pump was unavailable, etc).

Large traditional planked vessels sometimes were lost because they broke up in a sea. More commonly, they were simply overwhelmed and flooded, since they couldn't recover from an extreme knockdown.

Remember the ferry which sank in the Baltic a few years ago, with almost everyone aboard dying? Initial failure was the outer bow doors, which apparently weren't properly latched or the latching mechanisms failed. Then the inner doors failed. The bridge crew didn't know about the failures in time. The cargo (vehicle) deck didn't have adequate freeing ports. And like most ferries, a relatively small amount of flooding drastically reduced stability due to low initial stability and the free surface effect.

All of us are much more likely to sink because of a progression of failures rather than come some instantaneous immediate failure - unless it's being buried by a real monster. May it not happen. From that point of view the difference between large and small vessels isn't very important. It's true that a small boat is more likely to recover from a knockdown, but it's also more likely to be knocked down. The details matter in all vessel sizes - the sea will find and exploit the weak points.

[Ed Burnett]

I don't wish to be contrary here, however I would just like to correct something said above.

The main relationship when dealing with waves is a link between wavelength and wave speed:

Wave length = 2 x pi x (wave speed)^2 / g

(This is why displacement boats have a limiting speed. When the wave they generate is the same length as their waterline, the bow and stern systems superimpose and create a spike in the resistance curve. The link between wavelength and speed sets the boatspeed at which this occurs)

Wave height is a separate issue, but in general is limited to around 14% of wave length as a wave steeper than this will become unstable and break.

This all assumes the water is deep (deeper than half the wavelength). A lot of the most famous nasty bits of ocean are the way they are because os some underwater feature affecting the surface waves.

[ahp]

I just want to add to Ed Burnett's post. After the wind drops, the wave hights drop too, but the distance between crests remains the same. These are still very large waves, but in deep water they are now almost unnoticable because their slopes are very gentle and they are not breaking off. But when they get close to shore, look out! When they reach shallow water it seems like a wall of water rises out of nowhere.

[Tom Lathrop]

Like most who have sailed offshore, I've never experienced a big storm in a small boat and surely have no desire to. Fifty years ago I did have the pleasure of weathering two typhoons off Japan in a Gearing class destroyer. Being young and foolish, I had no fear since I had learned to trust the boat over almost three years in all kinds of conditions. Had I known then about other destroyers that had foundered in such storms, I'm sure things would have looked differently.

All the theoretical discussion of wave height, length, fetch, etc forgets that the wave you are looking at has something in common with the theoretical wave but is really made up of the sum of many different wave trains that add or subtract from each other. I well remember the swells that we ran through after getting out of one of the typhoons. They were extremely long and fairly high but not steep at all with smoth rounded tops. The helmsman had a hard time keeping the ship from slewing around and broaching as these fast swells overtook us, lifted the stern and sent the ship surfing down the wave front. And yes, there were few full stomachs aboard, and those with saltine crackers.

Sleeping was nigh impossible since many of the sleeping compartments were awash with seawater taken in through the upper deck ventilators. I would take my blanket and wedge myself in behind a radar or radio transmitter so that my body would stay in one place. It may be that a small boat is safer in those conditions but I want to be ashore when it howls like that. Standing on the bridge deck of a ship and looking up at streaking waves about to break on me holds the same fascination as staring at a cobra.

"A fool on a boat will soon be drownded, because he will go out into the sea on a day when he should stay in port. But I am not a fool and am only drownded now and again."

[John E Hardiman]

There have been some very good points raised here about waves. But let's tie it all back to Alan's original post about ship strength and how it affects building and design of ships and boats.

First let me say that I have the privilege of working on the edge of a major R&D project to answer this exact question. I can give you what is felt by my NA community to be best practice. As some of you may know, this means we put on our pointy hats, get locked in a room, and bash on each other until a "consensus" is reached. If anyone desires me to point to references to a specific of my summary, e-mail me.

A synopsis of current best practice in relation to the FITZGERALD and the DERBYSHIRE, and other losses.

The seaway is composed of at least two parts, the wave and the swell . The wave is the locally generated part and generally, for open water, is in the direction of the prevailing wind and gives the seaway its "rough" look. It is a function of fetch, duration of the wind, and wind speed. As was pointed out there is a limiting height, usually due to wind speed. Swell on the other hand, is formed remotely. Ocean storms thousands of miles away generate large, long period waves. When the storm dies, these waves roll on across the ocean basins at very high speeds, the longer period waves traveling faster giving the seaway a long rolling look. In a seaway, depending where you are and at what time of year, there may be no swell or several different swells, form different directions. As there is no single period to the sea way, a sea spectra is developed to measure this. From this sea spectra a significant wave height (Hs) is determined. By using statistical methods a most probable maximum wave is determined. However, there is a small, but real, probability of the ship encountering a larger wave. I like to call this a statistically significant event rather than "rogue" or "freak" waves. These things exist, and I believe that last year they blew the roof off a wave tank trying to make one.

Now, using our operational criteria , like operate in SS5 and survive SS8 for 24 hours, we use finite element analysis, energy methods, and elasto-plastic design to design the hull. Remember, there is still that statistically significant event out there that we except as an operational risk . Ships like the FITZGERALD and the DERBYSHIRE where most likely designed using deterministic methods much like Ross mentioned. In this method the hull is analysized as parts and statically . First the whole hull as a girder (primary bending) , then the compartments between bulkheads (secondary bending) , and finally the hull plating itself (tertiary loading).

What does all this mean? Remember, we said that large (ie long period) waves move at high speed? It has been noticed that the majority of damage occurs when the ship is heading into the seas. This is because the impact velocity of the wave into the hull plating is high. It is very common to see lightly plated ships with the plating failed between frames (the "hungry dog" look). There are actual cases of houses on supertankers 40m (~133 ft) off water being stove in. The wheel house and the recovered boat of the FITZGERALD show this as does the bow of the DERBYSHIRE. Of course the alternative is to run with the waves, but as large waves travel at high speed, you cannot outrun them and risk broaching to.

Additionally, remember that we said that the swell and the waves were separate. This includes direction. Sometimes huge cone shaped peaks are formed when the waves and swell are at near right angles to each other (Such as a storm in the Gulf of Alaska crossways with a swell from NZ). This is a common cause of loss to fishing boats. I think the University of New Orleans (LA. USA) did a very good job of describing this.

Finally, there is the geographics to consider. Given the prevailing winds, the east coast of the US is generally sheltered from the types of swell that that is common on the west coast. While it may look "rough" on the east and "pacific" on the west, the west coast actually has much more energy in its "average" seaway. In the southern hemisphere, the fetch is all the way around the world, and HUGE waves can be formed in the southern ocean.

In the final analysis, it is most likely that both ship were overwhelmed by waves that could neither be predicted or designed for. And most likely, all vessels can encounter such a wave.

Eternal Father, strong to save,
Whose arm hath bound the restless wave,
Who bidd'st the mighty ocean deep
Its own apponited limits keep:
O hear us when we cry to thee
For those in peril on the sea.....

[ 08-22-2002, 01:01 PM: Message edited by: John E Hardiman ]

[Alan D. Hyde]

Thank you, John.

"Oh Trinity of love and pow'r
Our bretheren shield in danger's hour;
From rock and tempest, fire and foe
protect them wheresoe'er they go;
Thus evermore shall rise to Thee
Glad hymns of praise from land and sea."

And amen...

Alan

[plimsol]

One further element in the design of large vessels is that they have to flex.If they did not, they would break apart from the forces inparted on them by the passage of the wave train. The trick is to design a vessel that will hog and sag, but not crack.
I sailed for several years on a tanker that was quite flexible, in fact she was too flexible and was sent to Japan to be stiffened up. On the return voyage, she hit a "hole" off the Aleutian Islands and cracked just in front of the pump room. Actually it was two cracks which each ran almost from one sheer to amidships. She returned to Japan very gingerly for more steel.
It is quite a sight to watch a 900 foot+ ship flex as it crosses the Columbia Bar. The forward third is hinging up and down, the midships is twisting clockwise and the stern section is torquing counter clockwise. The N/A's made the right decisions and she sailed for many more years until she was scrapped.

[mmd]

A nice reply, Mr. Hardiman. Were the results of your R&D project published by any of the professional society journals such as SNAME or RINA?

[John E Hardiman]

To plimsol;
You are correct, there is a structrual trade-off between the sectional modulus of the hull and the elastic modulus of the material. The idea is to load all the material in hull section evenly. Because the material further from the neutral axis has higher stress, those plates are thicker or higher strength or both. The same is true for most wooden craft, and so we see the keel/keelsons, wales, and sheer clamps.

To mmd;
Thank you, but I don't think there will ever be a paper. We are not so much breaking new ground, but rather redefining how to define ship and contract requirements. This study came after several ships/systems were built that didn't meet requirements and/or had failures. This happened because performance was specified in terms of NATO sea states. My orginization got called in to show how we did some successful designs. NATO sea states totally ignore the effects of swell. This is a parasitic effect of using SAR to get ocean wind/wave data coupled with the data reduction done to derive the Bretschnider and JONSWAP sea spectra development. My orginization was on the west coast so we knew that there was always a 3 foot/12-15 second swell and added it to any required sea state. So my community is looking for a more accurate way to include the effects of "all ocean" swell into the design.

[ 08-22-2002, 01:00 PM: Message edited by: John E Hardiman ]

[mmd]

Thanks for the explanation, John. Too bad the results of your research aren't publicly available. I am always interested in this type of data and analysis, even though it is not specifically relevant to the types of craft that I design. Little boats tend to hit things, roll over, or shake apart long before they have chance to bend. What was the old saw about knowledge?: "No knowledge is useless even if it is only tertiary."

[John E Hardiman]

mmd:
Actually you might be interested in one little point that fell out. For many years, "wave slap" was defined as 2000 psf (lbf/ft^2). However, a look at some common failures put it at ~5,000-10,000 psf depending on what and where. Over the last century, an analysis shows that on average we have seen 1-2 minor structural failures every year, a major failure every every 5 years, and a loss every 15 years. Of course, this includes personnel/tactical/navigational errors that leads to a problem.

[Dale R. Hamilton]

How about some comments on how this new condominium ship- "Freedom something" is going to fare at a million or so tons and a mile long? This damn nightmare is actually selling space and under construction. Will this be the biggect sea tragedy ever?

[mmd]

Dale, it may become reality, it may actualy work as proposed, it may even break even financially; I don't look upon it as anything other than a waste of resources. But please don't call it a ship - it is as much a ship as a jet-ski is a boat.

[John E Hardiman]

Dale;
Not my place to make comments on it even if I knew the design details. I suggest contacting Freedom Ship International (FSI) for more information. However, like the mile high buildings that have been proposed, I feel that the technology is at hand to build something like Freedom Ship. There have been several detailed floating airport studies (Toyko and SFO, for two) and there is the US Navy mobile floating causeway concepts. I think that like Brunnell's (sp?) GREAT EASTERN the ship may be ahead of it's time but if they can pull off the financing it could get built. They say it's not a tax dodge, but I've yet to see where they're going to flag it.

[ 08-22-2002, 06:04 PM: Message edited by: John E Hardiman ]

[Andrew Craig-Bennett]

Coming to this thread a little late, here are my observations on the question of the structural strength and integrity of modern bulk carriers, in response to Alan's request.

Let me say at once that I am not a Naval Architect. though some of my friends are. I am a director of a shipowning company who also lectures and writes a newspaper column on merchant shipping.

The "bulk carrier" referred to is not such a very old ship type. More correctly we should say "self trimming bulk carrier", with hopper shaped lower ballast tanks, saddle shaped upper ballast tanks, and, generally, corrugated bulkheads on stools, with steel hatch covers extending over the space between the saddle tanks.

Commercially, ships of this design have replaced the 'tweendecker for the carriage of most non-containerisable dry cargoes, apart from vehicles, paper reels, very large loads and special cargoes such as wood chips. The effect of canal and port restrictions is to funnel ships of this type into certain size ranges, such as

True lakers

Handysize Lakes - fitted deep sea bulkers (c.26,000dwt)

Handymax (c. 35,000 - 48,000DWT

Panamax (Panama canal capable) 63,000- 72,000dwt

Capesize (typically 150,000 - 180,000dwt)

The last named carries coal and ore, almost exclusively, Panamaxes carry these cargoes plus grain, lakers ditto, and the handysize and handymax, which unlike the others have cargo cranes, as a rule, carry any dry cargo - coal, ore, grain, steel sections, steel coils, timber, pipes, bagged rice, bulk raw sugar, fertiliser, cement - well, you get the picture.

These ship types started to appear in large numbers in the 1960's and by the 1980's they had effectively displaced the 'tweendecker from the primary tramp trades.

A very important point to note here is that the current Load Line convention dates from 1966 i.e. it reflected experience with 'tweendeckers, not self trimming bulkers. Please note, in particular, the hatch cover strength requirement which envisages a hatch being able to withstand 2.75 metres of water head.

Personally, I consider, in company with several eminent Naval Architects, that whilst this was adequate for 'tweendeckers of 12-16,000 dwt, it is inappropriate for much larger ships, espescially for bulk carriers built using the reduced freeboard permitted by the 1966 Convention.

Another point worthy of note is that dense cargoes, such as ore, are liable to shift, unless the self trimming ability of the bulk carrier's hold is utilised, and this can only be done if the hold is full. In order to allow this, without sinking the ship below her Load Line, alternate holds only are filled. This has an interesting effect on the shear force and bending moments acting on the vessel's structure....

Concerns have been expressed about the strength of these ships since the late 1980's. In fact a great deal of work has been done by the Classification Societies, led by LR, DNV and ABS, on the subject.

However, there is another factor which must be taken into account. A merchant ship exists to carry cargo at a profit. The less she costs to build, the better thye figures become, of course, so there is immense competition between the building yards to build such ships as cheaply as possible.

I regret to say that a great many Naval Architects are involved in "optimising" ship designs to use the minimum possible amount of steel, and the simplest possible shapes to fabricate, consistent with the letter, rather than the spirit, of the relevant Conventions. And unfortunately the Class Societies are dragged into this as well - they need business. The weight of steel in a modern ship is about 70% of what it was thirty years ago. Look at a modern ship and she has no forecastle - it is not required by the Rules, so it has been eliminated, although it certainly helps to keep the sea off the decks.

These ships lead a very hard life - it is usual for iron ore and coal cargoes to be tipped in from chutes at a speed which will load the whole ship in a few hours and for these cargoes to be discharged using thirty ton grabs, or larger, and for pneumatic hammers to be used to dislodge cargo hung up on the frames.

Only in quite recent times have any steps been taken to unify a standard for corrosion control inside ballast tanks. Most ships are still rotting rapidly from the inside out.

So, to answer Alan's question, yes, there is a problem.

[ 08-22-2002, 08:07 PM: Message edited by: Andrew Craig-Bennett ]

[John E Hardiman]

Thank you Andrew for your insight. I rarely get to see the commerical side of things.

When I went through school (78-84), there was a big push to use the new "cheap" ($25,000 for a true blue IBM PC) computers to get away from the classification society rules (the ABS paragraph used was 1.8 in my 1981 rules) which drove costs in the inflationary 70's. But I still remember the problems with the old finite element programs. You could get a piano wire to support a compressive load if you coded it wrong.

Correct me if I'm wrong, but I thought the design of the FITZGERALD was mid 60's vintage, and the DERBYSHIRE early 70's. Shouldn't both of these ships have been built to the rules? I knew the rules underestimated the very large ships (like the AMOCO CADIZ ground tackle) but I didn't think it would be that bad.

My 1981 ABS rules give the largest waterline variation (effectively a wave the ship length) to be designed for as 26.75 feet (8.151m). The largest wave height (trough to crest)I could expect on a 800' crest length would be ~114'. Indeed, the wave I would design for once in the life of a ship in SS6 would be ~72' (Hs=18'* 99% probibility =~4)

Hatch covers for the 1981 ABS rules are 358 psf (L>100m) with a safety factor of 4.25 on ultimate strength which works out to about 891 psf to yield. Even the load you give (2.75m) is only 572 psf. Allowing for a safety factor of 5, yield of the hatch cover would occur at ~1676 psf or a 26 foot head or a falling speed of 41 ft/sec ~24 knts. These loads are easily achieved by a large plunging wave.

As for your comment about rusting out, there have been many recent problems with materials. Like the ERIKA rust problem, the K-monel problem, The Ti 6-4 problem, and the 5083-H321 aluminum problem. We have had some problem getting EH32 to pass all the tests. I think it has to due with, as you pointed out, the profit margin driving the process, and some of these pocesses have very thin margins.

[Andrew Craig-Bennett]

The FITZGERALD is not a ship that I can offer any ueful comment on, but the DERBYSHIRE was a 162,000 DWT ore/bulk/oiler built in 1976, lost in a typhoon when laden with ore for Japan in 1980. The wreck was found and examined, quite recently, and the conclusion was that the forward hatch covers were stove in, possibly after the forepeak ballast tank had filled.

There have, alas, been many, many more losses, which did not involve British and American nationals. A frightening number of them have been ships which got off one distress message, then vanished, implying a catastrophic failure of the hull girder. There have also been cases of side shell plating detachment.

[Ron Williamson]

Big Fitz built in about 1957,wasn't she(or he?)?
R

[Andrew Craig-Bennett]

Thanks, that was very interesting. I am, as you will notice, tiptoeing delicately round a hugely controversial subject. Alas the media like stories with goodies (hardworking, deserving, white, British and American crew - I am trying to remember if I ever met any of those - I can remember plenty of stroppy, dirty, idle, drunken and drug addicted ones!) and baddies (wicked ship owners, espescially multinationals).

The truth is that the whole industry has gotten itself into a dreadful mess because it has effectively escaped all regulation, thanks to the flags of convenience, and has become the ultimate, dog eat dog, free market, with wafer thin margins for everyone. Since this means cheap ocean freight for all of us, nobody really cares too much about it.

This story is seen by the media as too complex for their readers, listeners and viewers to grasp - it takes more than a soundbite to get it over.

[mmd]

We here on the north-east coast of North America have seen the effects of such bulk-carrier failures too frequently in recent years, owing in no small amount to the vile winter conditions of the North Atlantic and the number of bulk carriers transporting our grain and iron ore to Europe. The incident of the Flare breaking in half off of Newfoundland a few years ago is a glaring example. I don't think that I can add substantially to the erudite comments above by John H. and ACB, as I haven't worked on "big ship" structures for over a decade, but wanted to throw my two bits in with the comment that among my colleagues when I was doing big steel design, it was common practice to "design to rule" using the ABS or LR rulebooks and to not give any consideration to past practices, failures, or to ask the fundamental question of "why is this done this way?". The rules were God and the priests' job was to interpret the rule of God with the least amount of welding. At times I wasn't very popular with my bosses for continually questioning the rationale behind this mindset. It was particularly galling when, in a roomful of a dozen or so NA's and NA Techs, I was the only one whom had any offshore commercial seatime, but my experiences and observations were discounted. On one occasion I was championing an arrangement change to enable the crew to access a service panel more readily while underway (it's location was fine while the ship was at rest, but a piece of ship's structure provided a real head-banger if you momentarily lost balance in a seaway; altering it's mount configuration to turn it ninety degrees would have eliminated the problem) and was dismissed with the comment that "the crew doesn't matter; after they hit their head a few times they will learn to hold on better". I strongly believe that it should be a mandatory requirement that future naval architects have at least three months of documented seatime on deep-sea commercial ships before they are allowed to practice their craft. I have worked for too many senior NA's who have never been in a boat bigger than 25 feet nor farther offshore than two miles.

[John E Hardiman]

Originally posted by mmd:
On one occasion I was championing an arrangement change to enable the crew to access a service panel more readily while underway (it's location was fine while the ship was at rest, but a piece of ship's structure provided a real head-banger if you momentarily lost balance in a seaway; altering it's mount configuration to turn it ninety degrees would have eliminated the problem) and was dismissed with the comment that "the crew doesn't matter; after they hit their head a few times they will learn to hold on better". LOL,,,,

We call those types "desk engineers" who complain when they have to put their steeltoes on to go to the drydock. It is sometimes strongly rumored that some of them do shipchecks from the window. :D .

Yes, I know my card says "seaman/wiper" and have seen the bar fights start over that ;)

[Andrew Craig-Bennett]

Originally posted by John E Hardiman:
</font><blockquote>quote:</font><hr />Originally posted by mmd:
On one occasion I was championing an arrangement change to enable the crew to access a service panel more readily while underway (it's location was fine while the ship was at rest, but a piece of ship's structure provided a real head-banger if you momentarily lost balance in a seaway; altering it's mount configuration to turn it ninety degrees would have eliminated the problem) and was dismissed with the comment that "the crew doesn't matter; after they hit their head a few times they will learn to hold on better". LOL,,,,

We call those types "desk engineers" who complain when they have to put their steeltoes on to go to the drydock. It is sometimes strongly rumored that some of them do shipchecks from the window. :D .

Yes, I know my card says "seaman/wiper" and have seen the bar fights start over that ;) </font>[/QUOTE]Ain't that the truth!

The last ship I was personally responsible for, from conception to delivery, was a Capesize bulk carrier built at Harland and Wolff and delivered in 1994. She represented a serious attempt to overcome the known weaknesses, cost a fortune, did my career no good and I am happy to say is still trading for her original owners. We had to fundamentally re-educate the yard after hearing comments like "Maintenance - that's the owner's problem, I'm not interested in that!"

(Reply - "You are talking to the owner's representative, and if you want this ship ordered, to say nothing of delivered and accepted you may like to re-consider!")

Ballast tanks were blasted to SA 2.5 and had 3 x 250 micron full coats and two stripe coats of CTE and pitguard anodes to make quite sure. Just passed her second intermediate, and the class surveyor said, "Best I have seen!" It can be done, but nobody will unless they are forced to.

[Alan D. Hyde]

I am enjoying this excellent interchange, and very much appreciate all the good contributions.

As far as I am concerned, this kind of thing is the Forum at its best.

Some years ago, when our oldest daughter was taking her transatlantic, I had a complete tour of the QE2: bridge, engine rooms (diesel and electric), prop shafts, everything. (How this was arranged is a long story, but can be summarized by saying that I had some talks with Frank O. Braynard, a great guy, and followed his advice).

Anyway, there seems to be little comparison between the way she was built, and the way that recent "cruise ships" are constructed.

Bulk carriers are not the only place where some cost-cutting looks to be going on. Any comments on the "cruise ships?" They don't seem likely to handle a substantial storm very well, and they're too slow (economics again) to get out of a storm's way very quickly...

Alan

P.S. The QE2, by contrast, dodged out of the way of hurricane, at 32 knots, while our daughter was aboard.

[ 08-23-2002, 11:46 AM: Message edited by: Alan D. Hyde ]

[Dale R. Hamilton]

All this erudite exchange make me expect a major sea going disaster when the "Freedom" raft is launched. You just know they are going to be more focused on selling units that building a safe structure. And from what I read- people are buying.

[John E Hardiman]

Originally posted by Alan D. Hyde:
Bulk carriers are not the only place where some cost-cutting looks to be going on. Any comments on the "cruise ships?" They don't seem likely to handle a substantial storm very well, and they're too slow (economics again) to get out of a storm's way very quickly...
Actually Alan, those cruise ships arn't that slow. That is if they drop the hotel load and apply it to power. As I pointed out in the '6kt airboat' thread, what they do is trade off main propulsion for hotel loads. A standard day is:
Cruise about at 5-6 kts in the sun so it's not very windy on the decks
Lots of lights from dusk to midnight at 5-6 kts for dancing on the decks
Flank ahead midnight to dawn at 20 kts to reach the next port while everyone is bedded down.

Remember, standing on the deck of the old UNITED STATES when she won the Blue Ribband would not have been fun as it would of been blowing at least 30 knts. The old liners like the QEII had an entirely different set of operating requirements.

[Alan D. Hyde]

My understanding is that the old France, which I sailed on in late fall of 1970, when she was still fast, has been de-powered, and will now only do 17 knots as the Norway. This is fast by tramp steamer or Liberty ship standards, but is certainly not in the "ocean greyhound" category.

It seems to me that speed can be an important element of seaworthiness.

And, if these vessels don't have the speed to get out of the way, do they have the stability and strength to stay afloat while fighting it out? I don't know, certainly, but I wouldn't be surprised if they weren't in some respects less strongly built than the bulk carriers. Or am I just unduly cynical and suspicious??? Many of them are ugly vessels, to my eye...

Alan

[John E Hardiman]

Alan;

One of the common misconceptions about modern ship management practice is that the ship is alone at sea with a captian as "Lord beneath God". In these modern days of GPS, weather satellites, cell phones, satellite communication, day trading bunker prices, weather and seaway models; the home office is just a phone call away. I know bainbridgeisland and he used to work for a large oil company in the early 80's. He said that they had routers (people who select a route) for every ship at sea; told them where to go, how to get around the storms, course for best speed, where and when to bunker for lowest price. The ship uplinked what it needed in terms of stores, food, fuel, maintainence, etc. so it would be waiting for the brow to touch down. I cannot see how a modern, well equipped ship could, or should, sail into weather trouble.

As an aside, I was just thinking about the Freedom Ship. Lets see.... ~60,000 people @ 7 lbs dry stores, 3 lbs reefer stores, 1.7 lbs frozen stores and 35 gallons of freshwater a day (call it all 300 lbs/person/day) is 18,000,000 lbs a day or ~8,100 tons plus another ~800 tons trash, lets say an even 9,000 tons a day.

!!!We need to start a shipping company!!! :D

[Alan D. Hyde]

John, is it not true that storms are sometimes much stronger than predicted, and go where they're not expected to, and also that sea states sometimes build far more rapidly than anticipated?

As long as there are humans involved, won't there occasionally be errors?

What I wonder is how much margin for such errors, in terms of strength and stability, is built into these vessels???

Alan

[John E Hardiman]

Alan;

There is always room for error, human or otherwise. If you are a true believer in the scientific method then you know that there is a small chance that tonight the world will stop spinning and the sun won't rise tomorrow. smile.gif

Seriously, I was once asked to design something that WOULD NOT FAIL. I told them that that was impossible, there is always some risk. As part of my job I write Damage Control Booklets. I was asked once if I had covered all casualties, again the answer was NO, I felt I had covered everything throughly, but how can I cover a casuality that I cannot forsee (sailors being a "creative" lot :rolleyes: )? Once an independent safety review looked at a system and determined that if it ran into something at flank ahead there COULD (their words, not mine) be damage to the system and a hazard to personnel. I laughed and said I didn't expect ANYTHING of the system to survive after a impact at flank speed. These are what I termed operational risks. They are to be minimized yes, but they cannot be avoided alltogether
As Voltare (I think) once said "Being aboard ship is like being in jail except you can drown".

[ 08-23-2002, 06:21 PM: Message edited by: John E Hardiman ]

[Donn]

I read this thread, more than half of which I cannot understand, and then I read about the coal carrying multi-mast ships built by my forefathers in the mid 19th century, and their spectacular losses along the coastline where I cruise in my tiny boat, and I realize how much commercial shipping has changed, and, at the same time, how little it has changed.

[Andrew Craig-Bennett]

I'm afraid that I don't have experience at first hand of the modern cruise ships; it is twelve years since I was closely involved with a cruise ship and she was no spring chicken then. She had about 16 knots, flat out, but she spent each summer in typhoon alley and never came to harm. She did have extremely capable senior officers and she only carried 520 passengers.

The theory of modern cruise ship design is that whereas the old passenger liners had their "public rooms" at the top and cabins lower down, and generally quite deep draft, because they sailed between big ports, the modern cruise ship, whilst much bigger, needs to get into "quaint" little places so she has shoal draft and is fitted with very clever azimuthing thrusters. They are diesel electric ships, and as John says the hotel load can be diverted, just as when a big containership drops her reefer load to run her thrusters for berthing.

Meanwhile because everyone likes an "outside" cabin, ideally with a private bit of deck, the public rooms are at the bottom and the cabins are at the top.

I should say that there is, currently, a great deal of concern being voiced, in marine insurance circles, about whether a serious accident to one such vessel might result in liability claims for death and injury on a scale too great to be paid under current arrangements.

It is also only fair to say that the safety record of cruise ships, as opposed to ferries, is amazingly good. All the bad passenger ship accidents of recent years, such as the ESTONIA, DONA PAZ, HERALD OF FREE ENTERPRISE, MOBY PRINCE, and the others, have involved ferries.

[Alan D. Hyde]

John, or mmd, or ACB, or ???

Is there, from a structural engineering point of view, much extra strength (or redundancy) in a typical cruise ship of recent construction, do you think?

I am inferring (perhaps wrongly) from the above comments that maybe there's not. And what of stability when the power to dynamic systems is off?

I'm not trying to be difficult.

I just know how many thousands of people there are on these things, and wonder how well they'd cope with unexpected bad weather or (God help us) with terrorists.

Alan

[ 08-26-2002, 11:54 AM: Message edited by: Alan D. Hyde ]

[John E Hardiman]

Alan;
Not to be rude or anything, but have you got an angle on this cruise ship thing? A class action we could get cut in on and make enough to buy that boat I've always wanted? You're beginning to sound like Ralph Nader sniffing around for another Corvair :D

A modern ship is designed to be a strong as it needs to be given the conflicting constraints of economics, safety, athestics, hydrodynamics, etc. Except for certian specilized hullforms not used in cruise ships, dynamic control systems are for passenger comfort, and do not control ultimate stability.

When you step back and look at the major casulties that define modern maritime practice ( BIRKENHEAD, ?(the emigrent ship without WT compartments that sank after a trivial collision off Newfoundland),GENERAL SLOCUM, TITANIC, EASTLAND, MORRO CASTLE, ANDREA DORIA & STOCKHOLM, ESTONIA, up to the the rash of minor fires and groundings in recent years) you see that the majority of losses are either due to collision or fire, generally leapfrogging each other. Each loss causes more rules as holes in the previous ones are found. Additionally; personnel actions and command decisions usually cause or compound the the accident.

A cruise ship is far safer than being in a car. The real issue is the enormity of the number of deaths that gives one cause to pause. I would guess that at least 1,000 people die each day by accidents. If 150 die in a plane wreck that's major news. What would be the reaction if 1,500 die in a shipping loss? (Or 4,000 die in a building collaspe? The real amazing thing is not that the towers collasped, but that they stood so long) This is what SOLAS and the IMO are looking to prevent. But, these rules will not help if crew makes errors, or abandons their duty (like that liner off Alaska several years ago or that similar one off Capetown).

Control Number: 782085759
ORG: National Transportation Safety Board RPTDATE: 9/1/81 NUM PAGES: 45
AUTHOR: Not Available IMOSRC: United States ENTERDATE: 8/20/97 REPORT TYPE: Final PORGNUM: NTSB-MAR-81-1

From 1970 through 1980, the National Transportation Safety Board investigated 82 major marine accidents. Thirty-three (40 percent) of these were collision accidents. The Safety Board initiated this study to examine a representative segment of ship collision investigation data based on the Safety Board's marine investigation experience. The study identifies some leading causes of ship collisions and assesses the results of the Safety Board's collision prevention recommendations made to Federal agencies and to maritime organizations. The study found that human error is the predominant cause of ship collisions and that specialized marine accident data which underscore the human factor in the cause of ship collisions need to be collected. The study recommends additional measures to increase the effectiveness of the ship's bridge watch team, and the collection of data concerning the human factors that contribute to the cause of ship collisions.

Document is available to the public through:
National Technical Information Service
Springfield, Virginia 22161.
Telephone: (703) 487-4650
World Wide Web: www.ntis.gov (http://www.ntis.gov)
REFERENCE NTIS PRODUCT ID: PB82-120205INF

[plimsol]

Just a minor point about the design of cruise ships from a non N.A. I believe the vessels fall into a general catagory that can be called volume centered vessels as opposed to the weight centered vessels of yesteryear.
A cruise ship is designed for a large internal volume, but does not really have to carry much weight, as humans can be considered to weigh 200 lbs, plus another 300 lbs of luggage. Consequently a different hull form and structure has evolved from the traditional passenger liner of the 20's -50's.
Occassionally cruise ships drydock in Seattle, usually after a grounding or for a shave and a haircut. It is amazing to see the beam-draft to superstructure ratio. Wide, long and shallow. The ships meet the legislated stability and safety criteria. They are probably better designed than ships in the past, but it should be noted that they are not crossing the North Atlantic or Pacific in the Winter. That truely would be the cruise to Hell.

A note: Maritime regulaions have evolved as a result of passengers and crew being drowned or burned to death in major disasters. Check the registry of your cruise ship, it will not be American. It will be a flag of convenience where the inspection laws may be weakly enforced, wages are low, and the ablity to evade legal remedies is high. The ship may be bright and shiny, but it is not necessairly safe. Try fighting a fire with an underpaid and undertrained crew with four or more separate languages. It is hard enough with one language and training.

[John E Hardiman]

Plimsol, you are correct that a cruise liner is volume limited rather than weight limited. however, this effect on hull form and stability is more subtle. Like the debate fostered in the late 19th century, most notably by Commodore Munroe and Herreshoff between the "plank on edge" and the shallow draft centerboarder, the deep heavy hull and the wide shallow hull are two different beasts but both designed to do the same thing. While the heavier deep hull provides a very wet ride in a storm, requiring a high freeboard, the wide light hull lifts and gives greater motion but less stress. I agree the heaver deeper hull will be able to maintain speed better, but that is not the design requirement of a modern cruise liner you are comparing it to. It's like comparing a pilot boat that needs to always be on station to a poontoon boat that's for the "good" days. Furtermore, high initial stability is not always a good thing. A "good" sea boat should have a roll period between 10-11 seconds and be dry forward. A shorter roll period is very tireing and dangerous due to the high loads it causes, a longer one spends too much time heeled to be comfortable. A dry bow is provided by having enough buoyancy forward to lift the bow with strong quarters to prevent hobby horsing. Given the weight distribution of a modern cruise ship (engines low, accomidations high) the houses are not too high because as you said, they are mostly volume. Sail area from the beam may be high, but that is irrelevant when in most severe weather cases, you will be heading into the storm, as opposed to keeping to a scheduled route as the old liners did. As a side note, modern CVN's are about the same length/beam/depth ratio for the same reasons; They want slow easy motions and to get into shallower harbours.

Your last point about the flaging is not as bad as you made it seem. While it is true that the flag has effects on the officer number and manning requirements, all vessels engaged in trade from the US must meet certian requirements and fall under USCG inspection and SOLAS requirements. With the major lines, I haven't seen anything that says that the crew who is supposed to respond to a fire (like one of the black gang or deck department) did anything wrong. I don't expect a bus boy from the pursers department to don a OBA and plunge into a compartment fire with a fog nozzle or AFFF. But my experience is USMM and military, so maybe somebody else can enlighten us.

[brian.cunningham]

from:
http://www.usatoday.com/weather/askjack/waoceans.htm


"The Pride Of Baltimore, a fine 137 foot schooner, was reportedly struck by a white squall. The 121-ton vessel sank about 240 miles north of Puerto Rico, casting the surviving crew members adrift for five days. The Toro, a Norwegian freighter picked them up at 2:30 a.m. May 19th, 1986.

"Here is an eyewitness account of the sinking: ‘A tremendous whistling sound suddenly roared through the rigging and a wall of wind hit us in the back. The Pride heeled over in a matter of seconds. The 70-knot wind pushed a 20 foot high wall of water into the starboard side. She sank in minutes.’"also...

Q: My dad told me once about a phenomenon called a "rogue" wave. He said that he recalled one striking an aircraft carrier and actually bending a corner of the flight deck. This might have been in the late '40s or so. Have you ever heard of this occurring? I have done some checking and found very little information on rogue waves thus far. Thanks in advance.

A: You've touched on a fascinating topic. The only extensive discussion of "rogue" waves that I've come across is in Willard Bascom's book, Waves and Beaches. I have the paperback published by Anchor Books in 1980. In it, he describes rogue waves as "great solitary waves whose crests tower above their fellows and scare the living daylights out of the luckless mariners in their path."

In brief, winds blowing across water create water waves. The waves you see in any part of the ocean are really made of combinations of trains of waves from many different places. At times, the crests of waves will come together in a way to combine into a bigger wave. At other times a crest and a trough will combine to make a smaller wave.

These combinations are random. Bascom cites the work of one scientist who examined the probability of the occurrence of large single waves. This work shows that one wave in 23 is twice the size of the height of the average wave in a location. One in 1,175 is over three times average height and only one in 300,000 is more than four times the average height. Also, such large waves last only a brief time and then shrink as the combined wave trains that make then continue their own way.

I had not heard of the incident your father describes, but Bascom has many in his book. One of the most hair-raising rogue wave stories describes what happened to the 81,000-ton, 1,000-foot-long liner the Queen Mary in late 1942 during World War II. It was loaded with 15,000 American soldiers bound for England when it hit a storm 700 miles off Scotland. Without warning, "one freak mountainous wave" hit the ship broadside. The ship listed enough for water to wash onto her upper decks. For a few seconds experienced seamen aboard thought the Queen Mary was going to roll over. But it righted itself and continued. Rogue waves have sunk other ships, including large ones. Bascom says rogue waves probably explain what happened to many ships that have disappeared without a trace.

I highly recommend his book for anyone interested in the oceans or the surf. It's great if you go to the beach and begin wondering why surf acts as it does.

It would also make good reading on a cruise for anyone who's scientifically minded.
I have "Waves and Beaches" and know of the picture they were talking about :eek: I was trying to find the picture online when I found that page.

[ 08-27-2002, 04:31 AM: Message edited by: brian.cunningham ]

[Andrew Craig-Bennett]

The best known "hole in the sea" phenomenon is found off South Africa and is caused by a strong current meeting the continental shelf; the case is well known and ships are now routed to avoid it. It filled the flying bridge of an RN cruiser in WW2, it bent the bow section of the (modern and extremely well built) cargo liner Bencruachan 15 degress downwards, and broke the containership Neptune Sapphire in half.

I am in a position to state that the risk of terrorist attack on cruise ships is taken seriously and some very capable people work in the field.

[Alan D. Hyde]

John, I don't have an angle; what I do have (I suppose) is a different approach philosophically. My profound apologies if I sound like Ralph Nader. I spent a day with him when I was a senior at Bates (1972) and it is my impression that the Corvair he castigated was more made (by him) than found...

I do tend to "overbuild." As I grow older, I am more cautious, and prefer a wide margin of safety, particularly when responsible for other people. I've sailed canoes through surf, and been in lots of swampings and capsizes when younger, and was always a strong enough swimmer that none of it worried me. But I did gain some respect for the power of waves, and the force of longshore and offshore currents.

Add great numbers of mostly older people, many of them not too fit, and some of them panicked and irrational, and it doesn't take a particularly strong imagination to visualize the chaos that could ensue were a cruise ship to go down.

I like some of Andrew's comments with respect to the last ship for which he was responsible. I'd rather see us build (within reason) the best vessel we know how, and recoup its costs over a long service life. I take the same approach with cars; I don't like econoboxes.

This, I gather, is not the economic approach taken by some recent shipbuilders. I don't mean to imply censure of you or other active N/A's. Clients want what they want, not what we think they should have. That's why I've personally phased out of the practice of law, and work mostly on my own account. This means I'm in agreement with my client 100% of the time... It's cost me lots of money, but--- most of the time-- I'm not sorry.

Alan

[ 08-27-2002, 11:39 AM: Message edited by: Alan D. Hyde ]

[Andrew Craig-Bennett]

Alan, I have to say that you will not find me aboard one of these modern floating pleasure domes, and I should mention that the USCG have intervened, quite forcefully, in the question of fire protection of ships built, as most now are, with an "atrium" .

There was, incidentally, a philosophical chasm betwen the USA and the UK on passenger ship fire protection. The USA believed that passenger ships should not be flammable, period. The UK believed that ships will continue to catch fire and must have sprinkler systems fitted. I have been out of cruise ships for a while now and I don't know if this is still an issue.

Certainly, the stability of many passenger ships is a bit "iffy", compared to a dry cargo ship.

The number of cruise ships where the deck officers will only consent to fill the swimming pool (= free surface, high in the vessel) if the ship has just taken fuel and most of the fuel tanks are pressed up is rather large!

On the other hand, I do emphasise that the safety record of the cruise lines in busines today is outstanding - probably one of the commonest claims is from some dimwit of a passenger, who, having over-imbibed, takes a header into the swimming pool only to find, for the reasons given above, that the pool is empty!

[plimsol]

John, I had to laugh when you described high initial stability and the qualities of good seakeeping. I spent six years years on a small hydrographic ship that lacked all of those qualities.
The first thing the private contractor who bought her did was remove a some of top side weight. She departed for a short cruise off the coast of Washington. When she returned, she went right into a drydock for rolling chocks, which I doubt made any difference.
She wil stilll be short, stiff, with a nasty corkscrew motion and a lack of any support forward for her overhang. Not a fun time.

[John E Hardiman]

It's late here and I just lost an entire post it took me an hour to write :mad: . I thought it was a good one. :(

Oh well... in quick summary..

To brian.cunningham
If I remember the findings correctly the PRIDE was hit by a microburst , a wind feature that has been responsible for the loss of several aircraft also. Additionally, one of the findings was that while the hull was true to the type, the deck openings had been changed and she downflooded quickly when laid on her beam ends. The waves really had little to do with the loss.
The carriers were dammaged in typhoons COBRA and VIPER in late 44/early 45. The flight decks were bent by waves impacting the bottom of the deck as they had open bows. This lead to the "hurricane" bows that were later fitted and are still used. There were also several DD's lost, known or assumed due to capsize. The findings were that the CO's didn't want to comtaminate the fuel oil bunkers and didn't ballast down. Almost all DD's that survived ballasted down. One DD did survive a 360 roll.
Haven't seen Bascom's book. We use Wiegel, Oceanographical Engineering. Has several pictures of the DUWKs in the surf. He was the UCB professor that had the project from the ACE to do the beach studies ~1942 through 1965. Would be interesting to get Bascom and see if what he has to say.

To Andrew Craig-Bennett:
I really wonder about a terrorist attack against the ship . All cruise ships are two compartment ships I believe, which is better than most mid-size combatants (engine rooms are too large). There is a lot of information about contact damage out there and I doubt that most attacks will be technically sophisticated. I rather expect an attack against the passangers.
I think the difference between the US and UK stance on fire was based upon different experiences. In WWII the US had a lot of experience with loss due to fire and the big loss of the LAFAYETTE (ex NORMANDIE) due to free surface effects. After WWII in 55 or 58 (?), there was a detailed look into cabin fires (it's in SNAME Trans.) Rather than deal with the stability issue, the solution was to prevent the spread of the fire by making the ship fire-proof.

:( Here I went into a long discussion on stability, slope of the righting curve and its effects, righting energy, lolling, etc. Now all gone to the ether... :( Maybe another day when I'm awake enough to push the right buttons.

To Alan D. Hyde
A short summary of what I lost to the ether was a discussion of the length of time a ship spends with the original owners, and the reasons an owner sells. Most ships have a life of ~25 years, and will be sold by the original owners when their future maintainence costs begins to exceede their net persent value. Additionally, many ships are built for long term charter, the requrements of which may drive the disposal of the vessel. If you built to lease to a charter that requires vessels &lt;10 years old, you sell the vessel at 10 years. This means that the older ships are passed down to owners less able to maintain them. This is why some flags have the reputations they do.
Finally, one must consider risk from an economic and moral point of view. People feel the risks involved with cruise ships, cars, planes, and skyscrapers to be manageable. They feel this way because of government intervention to dictate safety requirements like a Plimsol mark, and 30 minute fire safe doors. I remember from econ that if the cost is low enough, then great risk is accetable. What safety requirements do is increase costs to remove the most likely risks. How well this gets done is the job of the engineer, but there are still risks that cannot removed no matter how much is spent. You finally end up accepting those, and, as I do, say a prayer each time one of my ships goes out.

[brian.cunningham]

Thanks for clarifying that!

[Andrew Craig-Bennett]

John, I think you are quite right and any terrorist attack would, most likely, be directed against passengers. My main contact in the field, (Brigadier) Brian Parritt, loves doing a Power Point presentation in which he says, "Here is your best defence!" and up comes a slide of a Labrador dog - the dog in question being the first puppy to be bred specifically for explosives sniffing!

I agree with you about engine room size and I fear that an awful lot of one compartment merchant ships, such as bulk carriers and tankers, are not, in fact, even that, because the assumed permeability index for the ER space is too high. There are some rather curious assumptions about bulkheads, too. I remember putting a VLCC through a tank stagger test - the attending surveyor was more than happy with one metre difference in head, which rather disappointed us as the ship was a good one and we were all set to "do it properly!"

There's no doubt, ships have become far safer, but public expectations have changed too.

[Alan D. Hyde]

John, sorry your efforts got zapped. Thanks for taking the time and trouble to re-enter part of your lost reply. Your thoughtful remarks are illuminating.

John and Andrew, your suggestion that terrorists would attack the passengers and not the vessel seems reasonable to me. Sir Edward Coke said that "Pirata est hostis humani generis" (Pirates are enemies of the human race), and it appears that there are many similarities between the proper response to pirates, and that which we should make to terrorists. That we deal with a shipboard threat only adds to the similitude.

John, I agree that risk/benefit calculations must be a part of all this, as they are of almost everything we do. We tend to weigh the likelihood of a risk against its gravity. For example, if I take the canoe out sailing on a blustery day when the waves are getting pretty large, there may be a 20% risk that I'll capsize it and get wet: no big deal.

But if I take a young child with me on such a sail, there might be a 1% or 2% risk that even with a lifejacket on, he or she might suffer serious harm. Therefore, though the likelihood of the risked event is small, its gravity may prevent me from incurring that risk.

There is another factor with ships and planes. We all know that the variation in skills and abilities between the top and bottom of ANY profession is very substantial. When we drive a car ourselves, or pilot our own vessel, we take responsibility for our own safety. If we get into trouble it's likely to be our own fault. And, since we're in charge, the way out of trouble is up to us.

In boarding a commercial airplane or vessel, we put ourselves pretty much at the mercy of its designers, builders, owners, and operators. Do we have a deft, top-of-his-profession Captain, or a drunk lacking one more mistake before he's pushed out the exit door? Most passengers simply don't know.

I've been very impressed with the calibre of the several Cunard (QE2) skippers whom I've met. I've never taken a cruise ship, so I have no experience there. But much rests with the capabilities and judgment of the Captain. Sam Morison has a good discussion of the destroyers mentioned, and their Captains' handling of the typhoon ("History of United States Naval Operations in World War Two," 15 vols.).

John, there may be a way to recover your lost material (a friend found 20+ pages for me once, but I can't say how he did it). I'd be interested in those discussions if they can be recovered hiding in some remote corner of your computer.

Thanks to all posters here for a thread which is (at least for me) generating lots more light than heat...

Alan

[John E Hardiman]

Sorry Alan, it's gone. I spent about 20 min. trying to find it, but seems to be buried as a memory temp file in the IE5 app, it created no footprint on the disk or in the profile (Win 98). I guess I could have done a virtual core dump to a text file and then done a bit search, but the muse was gone and so was the six pack. ;)

I do remember one thing now. I found it strange that other people would find the esoteric calculations to use a safety factor of 3.6 vice 3.5, or the rumuniations of four NAs sitting around a table of interest.

[ 08-28-2002, 10:38 PM: Message edited by: John E Hardiman ]

[NormMessinger]

Ha! Even though he didn't understand a word of it this old Thresherboy enjoyed and appreciated every bit of it. (Eat your hearts out "Miscellaneous Rabble.")

--Norm

[Ed Harrow]

Norm, you're right. I've been trying to keep up with this one, but following the bard's advice,

"One is only perceived wise by saying nothing".

[Andrew Craig-Bennett]

Beyond the abstruseness of NA's lies another esoteric world - that of the marine engineers. For years and years they assured us that you could never put more than 40,000 HP down a single shaft, and suddenly they have decided that 100,000 hp is perfectly all right!

Whilst we are about it - John - what's your view on current designs of double hull tankers?

[NormMessinger]

Yes, and tell us about the size of the shaft required to transmit 100,000 HP and the alloy required. --If you please.

--Norm

[John E Hardiman]

Originally posted by Andrew Craig-Bennett:
Beyond the abstruseness of NA's lies another esoteric world - that of the marine engineers. For years and years they assured us that you could never put more than 40,000 HP down a single shaft, and suddenly they have decided that 100,000 hp is perfectly all right!

Whilst we are about it - John - what's your view on current designs of double hull tankers?I'm sorry, I didn't mean to exclude MEs (being a NA&ME myself), rather I was thinking about conversations between me and my co-workers. Some conversations are so above me that I know I lose brain cells from lack of oxygen smile.gif .

Otherwise, I took a quick peek into Janes just to confirm what I thought. I don't know what type of horses you use over there but on this side of the pond we went to 50k/shaft pre 1940, 60K/shaft in '43, and 70K/shaft by '52. Is there more to that story?

I'm not really in a position to discuss minutia in tanker design. I can’t really recall which of the two competing standards won. I will say though that I think that putting a void on the outside will prevent a lot of minor, but public spills, that occur from docking, tugs, minor groundings, etc., because tanker skins are so thin for their tonnage. If I remember correctly, they where considering a tank depth of 5% of beam. I think this is too little for a major collision given tanker structure. So from the overall picture you won’t prevent another TORRY CANYON, AMOCO CADIZ, or EXXON VALDIEZ, but you will prevent a lot of oil in harbors. And yes, I know there is a maintenance issue with using them for saltwater ballast.

[Andrew Craig-Bennett]

I was thinking merchant ships. The earlier big containerships were built twin screw for fear of exceeding what "prudence" dictated. And of course they were mostly steamers. Just about all gone now.

Of course, ports have been dredged to take the latest behemoths.

I operated single hull tankers up to 280,000 dwt and we never had a leak through the hull. We did have a spill caused by a ballast pipe passing through a bunker tank (really silly design, but very, very common even in the best shipyards) and a pinhole leak in the pipe.

The idea of anyone inspecting let alone maintaining a six foot wide space, seventy feet down, seems improbable to me and there are also issues with greatly accelerated corrosion of inner tanks (maybe because the oil does not cool, nobody really knows yet) and in some designs there is a real issue, which Chevron have highlighted, with damaged stability.

Still, the politicos know best and Europe has followed the USA into double hulls.....

[Trog]

Okay.

Methinks my brain exploded.

Great thread.

[ 08-30-2002, 11:36 AM: Message edited by: Trog ]

[John E Hardiman]

Originally posted by Andrew Craig-Bennett:
Of course, ports have been dredged to take the latest behemoths.

I operated single hull tankers up to 280,000 dwt and we never had a leak through the hull. We did have a spill caused by a ballast pipe passing through a bunker tank (really silly design, but very, very common even in the best shipyards) and a pinhole leak in the pipe.

The idea of anyone inspecting let alone maintaining a six foot wide space, seventy feet down, seems improbable to me and there are also issues with greatly accelerated corrosion of inner tanks (maybe because the oil does not cool, nobody really knows yet) and in some designs there is a real issue, which Chevron have highlighted, with damaged stability.
I think here are the two points which make the concept of double hull different on each side of the pond. Harbor depth and tanker size. Europe is relatively compact with relatively shallow harbors. The US is spread out with a few deep harbors spread around and many shallow ones. Correct me if I'm wrong, but doesn't Europe move most of it's oil by pipeline after it comes in, either from the North Sea (by pipeline) or the Persian Gulf (by VLCC's) to offshore terminals. In the US, most of the product is distributed by train/pipeline in the east (WWII vintage) and by smaller product carriers and barges in the west, mid-west rivers, and gulf. Oil comes in to the US from both the North Slope and the Persian Gulf in tankers (the Gulf Coast is mainly pipeline with some Floating Production Platforms), but we have many more oil wharves than offshore terminals. I agree that a VLCC that uses a FPP or mono-point moor should never have a hull breach, but that is not the majority of sceaniros in the US. I get the feel from the marine industry news periodicals that incidental damage is more common over here.

As far as tank corrosion goes, alternately filling and draining a tank that's next to a warm oil tank with saltwater requires a good protection system. I myself would go ahead and pay the money to flame spray aluminum then plasma coat. But again this gets back to how long is the original owner going to keep the ship. Maybe we need to make it like the toxic chemicals and their containers here in the US. The manufacturer pays for the disposal of the container/material up front, so the user doesn't just dump it because of the disposal costs. As a side note, I opened voids on the IOWA in '85 that hadn't been opened since '43. %O2 was ZERO in the voids. There was no paint, no pitting, just a fine covering of rust "hairs" ~1-2 inches long. The only place not covered with these fibers were the assembly chalkmarks.

I saw the Cheveron paper also. There are many ways to design compartmentation for a ship, and some will give specific solutions to specific problems. You can also bound an investigation to give the answer you want, like some of the high-speed ferry wake papers that have been done recently. I think we are far from the last person speaking on the subject. :rolleyes:

[plimsol]

The next step is the development of double brained crew to go with double hulls. This would ensure that if the first brain failed the backup one would take over. Then again there is the definite possibility of compounding the error.

[John E Hardiman]

Originally posted by plimsol:
The next step is the development of double brained crew to go with double hulls. This would ensure that if the first brain failed the backup one would take over. Then again there is the definite possibility of compounding the error.Old hat... Navy already has it. One's called the OIC and one's called the OOD. smile.gif

[Terry Etapa]

As a side note, I opened voids on the IOWA in '85 that hadn't been opened since '43. %O2 was ZERO in the voids. There was no paint, no pitting, just a fine covering of rust "hairs" ~1-2 inches long. The only place not covered with these fibers were the assembly chalkmarks.
John - So, the O2 was all used in the reaction creating the rust? I once read in one of my welding texts about the use of inert gases used inside tubular structures to prevent corrosion. Is this a technique used in the marine industry?

[John E Hardiman]

Originally posted by Terry Etapa:
[QB
John - So, the O2 was all used in the reaction creating the rust? I once read in one of my welding texts about the use of inert gases used inside tubular structures to prevent corrosion. Is this a technique used in the marine industry?[/QB][/QUOTE]

Yep, some of these voids were between the belt and FO tanks, 60'x4'x15' tall and took ~24hrs to ventilate with a 6" blower. You could hear them suck when you pried the manhole covers off.

I can't recall any inerting for corrosion but there may be. A lot of times, electronic bottles, or optics, will be N2 purged to fight condensation and or water shorts, but not for corrosion. You may want to ask the guys that work on the rigs, They must do something inside the legs.

We have found that the best method is to paint EVERYTHING, anodes and cathodes; or to paint NOTHING (anodes meaning the less noble material site, not a specially applied zinc). What happens is that a nick in a coating system forms a cell with the zinc. A small cathode (i.e. everything other than the zinc) with a large zinc will cause a pit to grow at the cathode due to the large current flux. The idea is to get the areas on the anodes and cathodes near equal. Remember, zincs work because the electric potential between them and the failed coating, the further the distance from the less zinc the less potential due to the resistance of the material. Two areas of failed coating my have a lower resistence between themselves than to the zinc and will set up their own cell (this is especially true between the splash zone and the keel due to O2 levels). And so you can have a hole drilled through your plating and a nice bright shiny zinc. tongue.gif

[Andrew Craig-Bennett]

John, Europe has adopted the same double hull legislation or near enough the same, Funnily enough, I had just the same picture of tanker operations, in reverse! From over here I see the US East coast consisting of shallow harbours, unable to take a fully laden VLCC, so that the Arabian Gulf cargoes, moving round the Capoe of Good Hope in ULCCs and VLCCs, almost all go into the Louisiana Offshore Oilport ("LOOP", in the trade parlance) and the balance of crude imports, from Latin America, West Africa and the North Sea, travels in smaller ships, typically "Suezmaxes" of one million barrels capacity and say 140,000 dwt, as against the two million barrels of the standard 280,000 dwt VLCC.

Europe has several deep water tanker ports, from the Scandinavian fjords like Brofjorden in Sweden, where depth is obviously no problem at all, through the flooded rias on the west coasts of Ireland, Wales, France, Spain and Portugal to the dredged ports of the North Sea such as Europoort, Rotterdam, which will take a 50,000 tonner.

The Far East is draft limited by the 19 metres available through Singapore Straits, so we find little bigger than VLCCs trading that way from the Arabian Gulf.

Where Europe does badly is in dirty product trades, where the very high port dues tend to discourage the use of modern larger ships - the ERIKA is a case in point. She was an old banger hauling 30,000 tons of carbon black.

[Evan Showell]

Though slightly off-topic, I'll add my $0.02 regarding vessel operations, not design. The observation concerns a container ship. I'm not an NA, nor am I in the commercial shipping field so my experience and observation is, in fact, extremely limited.

I am an attorney by trade. I have done some marine cargo insurance work. In a recent case involving a containership that lost several million dollars worth of cargo over the side in a winter North Pacific storm I can say the following. In a deposition, the first officer, a twenty-something south asian gentleman was not familar with the concept of fetch. it would appear that the containers were improperly stowed based on the stowage plan and incredibly short time in port. The captain seemed hell bent on driving the course suplied by Ocean Routes even though it put the ship in the teeth of a storm for fear of deviating from the preordained delivery schedule -- I guess a price of "just in time delivery." That a captain or crew might be dissuaded from taking evasive action to avoid a storm for fear of deviating from schedule seems a frightening prospect.

Although in this case the result was only a few million in cargo lost, it could have been a lot worse. Are the margins in commercial shipping truly so thin that a company might risk losing a cargo or hull for the sake of on-time delivery? If so, the industry is in worse shape than I feared.

[Andrew Craig-Bennett]

Originally posted by Evan Showell:
Though slightly off-topic, I'll add my $0.02 regarding vessel operations, not design. The observation concerns a container ship. I'm not an NA, nor am I in the commercial shipping field so my experience and observation is, in fact, extremely limited.

I am an attorney by trade. I have done some marine cargo insurance work. In a recent case involving a containership that lost several million dollars worth of cargo over the side in a winter North Pacific storm I can say the following. In a deposition, the first officer, a twenty-something south asian gentleman was not familar with the concept of fetch. it would appear that the containers were improperly stowed based on the stowage plan and incredibly short time in port. The captain seemed hell bent on driving the course suplied by Ocean Routes even though it put the ship in the teeth of a storm for fear of deviating from the preordained delivery schedule -- I guess a price of "just in time delivery." That a captain or crew might be dissuaded from taking evasive action to avoid a storm for fear of deviating from schedule seems a frightening prospect.

Although in this case the result was only a few million in cargo lost, it could have been a lot worse. Are the margins in commercial shipping truly so thin that a company might risk losing a cargo or hull for the sake of on-time delivery? If so, the industry is in worse shape than I feared.Evan, you are dead right. Yes, they are. Many years ago, container ships were "expected" to arrive at the pilot station after a trans-Pacific crossing within 20 minutes of the estimated time of arrival (ETA) "or else" and the "or else" was, back in those more civilised times (I speak of 15 years ago) demotion for the Master.

The "problem" is in fact US railway timetables; the ship has to berth to meet the double stack trains' scheduled departure times, and yes, every Line now sells cargo space on "just in time" delivery.

Of course, insurance is quite cheap....

[John E Hardiman]

Evan & Andrew;
I was under them the assumption that a 1-2% loss each year of containers was more acceptable than the old rate of 4-5% "spoilage" of the break bulkers. I know the ISO fitting won't hold a 10 high stack in a boarding sea.

[Andrew Craig-Bennett]

Yes, and that was an advance on the sailing ship....but there is a real issue here. The tonnage measurement convention has had the effect of driving containership design down the route of minimal freeboard and maximum deck stow, whilst the post-Panamaxes have wide beam and mimimal ballast tank arrangements compared to older generation containerships. Consequently they are far more likely to shed deck stacks, and do shed them, compared to the containerships of a few years ago.

[John E Hardiman]

So; do we need to bring back the old shelter deckers, tonnage ports and all? :D

[Andrew Craig-Bennett]

Well, John, I do not think I would go that far!

But how about charging port dues on the amount of cargo handled in the port, or maybe even on the amount of quay space, deep water, etc taken multiplied by time in port?

Beyond containerships there are other similar absurdities in the shape of tankers with cut down afterdecks, awash likea half tide rock, ro-ro's and PCC's with the weather deck almost at the waterline, etc.

[Ross Faneuf]

I'm really enjoying this discussion, and desperately trying to match my vague memories from getting an NA degree 35 years ago (but I've written software instead as a career) with up-to-date expertise.

So tonnage openings and shelter decks are long gone? My professor had the hardest time trying to explain those, since they seemed so unsafe and weird.

Not discussed yet, but as I recall the really scary numbers are for ferries, and the larger the ferry the scarier the numbers. We did a vehicle ferry as a design project, and I could hardly believe the numbers - low initial stability, low ultimate stability, disastrously susceptible to loss of stability and capsize due to free surface effect of minimal flooding of the main vehicle deck - has any of that changed?

[John E Hardiman]

Unfortunately not Ross, ship hull form is still driven by outside forces. Though I have been in military construction since ~86, I still follow what happens in the real world. Generally, the idea is to maximize profit from a hull. The rules (ABS, DNS, LR, etc.) and the fee structure for a given route drive the hull to a particular form. Just like the old shelter deckers, the idea is to maximize cargo weight/volume for minimum cost. This is especially true for shipments between countries where the shipper pays a fee based upon net tonnage delivered.

One of my senior projects (1983) was an inter-terminal container ship of 500-1000 TEU. I chose to use a LASH ship (float on barge) hull form where the house was way forward, the medium speed diesels were right on the tank top aft, the main deck and hatch covers were slightly above the DWL and the rest of the stack was in the "well deck" between the ballast wing walls and above in guide frames. I'd have to look it up, but this design had a net tonnage of &lt;20% gross tonnage. You could get away with this as it was self freeing out the stern and you "assumed" the containers were tight. But it had a lot of freeboard forward. :D

[Andrew Craig-Bennett]

There have been new rules for ferries, driven mainly by the UK after the Herald of Free Enterprise and by Sweden after the Estonia. Basically, a new stability requirement which includes a longitudinal bulkhead on the lowest deck to cut down free surface, sponsons to improve stability, and better doors. Fiddling whilst Rome burns some may say.

[Andrew Craig-Bennett]

This thread has made me think. I really would like to know, from those who are not "in the business", if you think that shipping is a really daft industry?

For example, the "tonnage hatch" which John refers to was a little hatch opening which could not be closed with a hatch cover. This mystically converted the upper tween deck into an "open shelter deck" and reduced the ship's tonnage, on which she paid her port dues.

Similarly, the reason why roll-on roll-off ferries are so very prone to sudden and disastrous capsize is that their weather deck is so close to the water's edge; these ships developed from train ferries which had the weather deck much higher but could carry less load; to increase the cargo capacity the weather deck was lowered....

Is this, by the standards of other businesses, an industry run by mental defectives? I suspect that it is, and would really like to know!

[formerlyknownasprince]

Far too many industries end up introspective and relying on the lowest common denominator. Unions base their existence on protecting the weakest link, management look for a cosy existence, etc. Bureaucrats are sometimes worse - don't take a decision and you can't make a mistake that can be sheeted home to you.

[Scott Rosen]

My layperson's perspective is that the idustry is based a lot on tradition and evolution of craft. The ability to change is limited because the cost of change is so high and the time needed to make the changes so long. I wouldn't say it's daffy, just shakled by its own history.

I liken it to real estate law.

[Ian G Wright]

Andrew,
Big Cats = Big Wash.
I never did find out why, or how, Stenna get away with running at speeds such that their wash has killed small boat users miles away,,,,,,,,, but a dozy motor boat owner on the Crouch was castigated for running at more than 8 knots and spilling the morning coffee of a boat on a RCYC mooring.
Any idea?

IanW.

[bainbridgeisland]

Great thread. Just got back from vacation and haven’t seen it till now.

With respect to the new double hull tankers: Tankers are thin skinned ships. A single skin Ultra Large Crude Carrier (ULCC) of 450,000 ton capacity only has ½” thick plating. This skin plate thickness is driven by ship girder considerations rather than by collision or impact requirements. However, the single skin ship may survive impacts better than a double hull ship. The reason for this is that impact resistance is related to the amount of material affected by the impact. Thus thick skins (1/2” plate) tend to resist impact better than twin, thinner, skins on the double hull ship.

This was one of the arguments against double hull tankers from years ago. I have never worked on any of the double hull tankers, so I really don’t know if this problem was ever resolved. Since one object of the double hull tanker was to create a more damage tolerant ship, I think politics got in the way in this case. Some groups in our society were so adamant in their thinking that double hulls would protect the environment that they won despite physics and engineering not agreeing with them.

[NormMessinger]

"...they won despite physics and engineering not agreeing with them."

Now that is a common thread in our society, not just with enviornmental themes, eh? Don't let the facts interfere with a good bias.

--Norm

[Andrew Craig-Bennett]

Originally posted by Ian G Wright:
Andrew,
Big Cats = Big Wash.
I never did find out why, or how, Stenna get away with running at speeds such that their wash has killed small boat users miles away,,,,,,,,, but a dozy motor boat owner on the Crouch was castigated for running at more than 8 knots and spilling the morning coffee of a boat on a RCYC mooring.
Any idea?

I fancy it is called "lobbying", Ian. I do know for a fact that the Harwich Harbour Master and his staff were, and I daresay they still are, rather on the small boat side of the argument, but as Bainbridge Island and Norman point out, engineering and science come a good last in these affairs.

IanW.